A cation-pi interaction in the binding site of the glycine receptor is mediated by a phenylalanine residue.
Cys-loop receptor binding sites characteristically contain many aromatic amino acids. In nicotinic ACh and 5-HT3 receptors, a Trp residue forms a cation-pi interaction with the agonist, whereas in GABA(A) receptors, a Tyr performs this role. The glycine receptor binding site, however, contains predominantly Phe residues. Homology models suggest that two of these Phe side chains, Phe159 and Phe207, and possibly a third, Phe63, are positioned such that they could contribute to a cation-pi interaction with the primary amine of glycine. Here, we test this hypothesis by incorporation of a series of fluorinated Phe derivatives using unnatural amino acid mutagenesis. The data reveal a clear correlation between the glycine EC(50) value and the cation-pi binding ability of the fluorinated Phe derivatives at position 159, but not at positions 207 or 63, indicating a single cation-pi interaction between glycine and Phe159. The data thus provide an anchor point for locating glycine in its binding site, and demonstrate for the first time a cation-pi interaction between Phe and a neurotransmitter.
Pless
Stephan A
SA
School of Biomedical Sciences and Queensland Brain Institute, University of Queensland, Brisbane, Queensland 4072, Australia.
Millen
Kat S
KS
Hanek
Ariele P
AP
Lynch
Joseph W
JW
Lester
Henry A
HA
Lummis
Sarah C R
SC
Dougherty
Dennis A
DA
D024322:Amino Acids, Aromatic / Q000737:chemistry; D000818:Animals; D001665:Binding Sites / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D002412:Cations / Q000737:chemistry*; D005998:Glycine; D006801:Humans; D008845:Microinjections; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed / Q000379:methods; D009865:Oocytes; D010649:Phenylalanine / Q000378:metabolism*; D011485:Protein Binding / Q000235:genetics / Q000502:physiology; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011869:Radioligand Assay; D018009:Receptors, Glycine / Q000235:genetics*; D013329:Structure-Activity Relationship; D014982:Xenopus laevis
D024322:Amino Acids, Aromatic; D002412:Cations; D018009:Receptors, Glycine; D010649:Phenylalanine; D005998:Glycine